1. Field of the Invention
The present invention relates generally to a by-pass valve device used in a gas turbine combustor and more specifically to a by-pass valve for controlling a compressed air flow rate to be supplied into a combustion area of a tail tube downstream side so as to obtain an appropriate fuel/air ratio for a good combustion efficiency and for preventing foreign matters from coming into the gas turbine combustor for a smooth operation thereof.
2. Description of the Prior Art
As shown in FIG. 9, in a gas turbine combustor 01, fuel F is jetted into a combustor inner tube 02 from a fuel nozzle 03 to be led into a combustor tail tube 05. At the same time, compressed air PA discharged from a compressor 04 is led into the combustor tail tube 05 for combustion in a combustion area downstream of the combustor tail tube 05 so that a high temperature high pressure combustion gas CG is generated. This combustion gas CG is set to a flow velocity and a flow direction of designed condition by a stationary blade 06 downstream of the combustion area to be supplied to a moving blade 07. Thus, the compressor 04 is driven and a surplus drive force is used outside.
The compressed air PA from the compressor 04 is also supplied into the combustor inner tube 02 so as to form a mixture with the fuel F supplied from a fuel nozzle for flame holding in the fuel nozzle 03. This mixture is fired as a holding flame.
Thus, the fuel F jetted from the fuel nozzle 03 is ignited by the holding flame in the combustor inner tube 02 and is supplied into the combustion area with a fuel rich concentration.
On the other hand, the compressed air PA, except that supplied into the combustor inner tube 02 as mentioned above, discharged from the compressor 04 into a turbine casing 010 is supplied into the combustor tail tube 05 via an opening provided within the turbine casing 010. A by-pass valve 08 is provided in the opening near the combustor tail tube 05 and the compressed air PA supplied into the combustion area through the opening has its flow rate controlled by opening and closing of the by-pass valve 08. Therefore, a mixing ratio of the fuel F supplied from the combustor inner tube 02 and the air PA is adjusted to such a ratio as is able to generate a combustion gas of the best combustion efficiency in the combustion area.
As shown in FIG. 10(b), the combustor tail tube 05 is provided in 20 pieces along the circumferential direction of the turbine casing 010, and the by-pass valve 08 is provided in one piece for each of the combustor tail tubes 05. The by-pass valve 08 is operated to be opened and closed by rotation of a drive shaft 09 provided for each of the by-pass valves 08.
That is, as shown in FIG. 9 and FIG. 10(a), which is a partially cut out perspective view of a mounting portion of the by-pass valve 08, the drive shaft 09 has its proximal end connected to an end portion of a stem of the by-pass valve 08 and the drive shaft 09 passes through the turbine casing 010 so that its distal end projects outside of the turbine casing 010. As shown in FIG. 10(b), the drive shaft 09 is arranged in 20 pieces radially around a central axis of the turbine casing 010.
An inner ring 011 is fixed to an outer circumferential surface of the turbine casing 010, and an outer ring 012 is provided on the inner ring 011 and is moveable by an actuator. The drive shaft 09 is connected at the distal end to a side surface of the outer ring 012 via a link mechanism. When the outer ring 012 is rotated on the inner ring 011, all the drive shafts 09 are rotated so that all the by-pass valves 08 are opened and closed in unison. Thus, the compressed air PA is supplied uniformly into the combustion area downstream each of the combustor tail tubes 05.
In the prior art gas turbine combustor 01, the by-pass valves 08 are opened and closed in unison for controlling the flow rate of the compressed air
to be flown into the combustor tail tubes 05 provided in 20 pieces along the circumferential direction of the turbine casing 010 so as to adjust the mixing ratio of the fuel F and the air PA to be supplied into the combustion area between the combustor tail tube 05 and the stationary blade 06 for a good generation of the high temperature high pressure combustion gas CG. As a result, the structure is made such that the drive shaft 09 for opening and closing the by-pass valve 08 projects outside of the turbine casing 010 and such that the drive shafts 09 of as many as 20 pieces are arranged with substantially equal pitches along the entire circumference of the-turbine casing 010, as mentioned above, and this results in a problem.
That is, as shown in portion A of FIG. 10(b), in a type of the gas turbine casing 010 which is formed by an upper portion and a lower portion fastened so as to be integrated, a turbine casing horizontal flange 013 for fastening the turbine casing 010 and other like portions on the outer side of the turbine casing 010 interfere with some of the drive shafts 09 so that there arises a case at some positions where the drive shaft 09 for opening and closing the by-pass valve 08 can not be provided.
That is, the turbine casing horizontal flange 013, a by-pass pipe 014, etc. on the outer side of the turbine casing 010 prevent some of the drive shaft 09 from projecting outside of the turbine casing 010. Thus, the by-pass valve 08 provided in the corresponding portion within the turbine casing 010 can not be operated to be opened and closed by the drive shaft 09 which is operated from outside of the turbine casing 010.
Accordingly, the by-pass valve 08 which is provided in the circumferential position where the turbine casing horizontal flange 013 and the like interfere and can not be opened and closed by the drive shaft is set to a predetermined opening position prior to operation of the gas turbine and the operation is done continuously with this predetermined opening. Hence, in the combustion area of the specific combustor tail tube 05 of the gas turbine combustor 01, the combustion efficiency becomes worse which results in a problem that lower operation of the worse combustion efficiency is unavoidable for a whole of the gas turbine combustor 01.
Also, in order to solve this problem, if all the by-pass valves 08 provided in 20 pieces with equal pitches along the circumferential direction of the turbine casing 010 are constructed to be opened and closed uniformly so that the combustion in all the combustion areas downstream of the combustor tail tubes 05 is done efficiently to enhance the combustion efficiency as a whole of the gas turbine combustor 01, then such a structure in which all the drive shafts 09 for opening and closing the by-pass valves 08 are arranged so as to project outside of the turbine casing 010 is unavoidable. This results in the restrictions in the outside structure of the turbine casing 010 and creates a problem in the arrangement of a plant comprising the gas turbine combustor 01.
Also, in the gas turbine combustor 01, when the by-pass valve 08 is opened so that the air is led into the combustor tail tube 05 through a by-pass duct 015, foreign matters are liable to flow through the by-pass valve 08, which results in a problem that the gas turbine may be damaged thereby. That is, if supporting members of pipings and the like in the combustor are damaged by vibration, or if bolts, nuts and the like loosen to scatter, then foreign matters caused thereby enter the by-pass ducts 015 to be led into the gas turbine, which may result in serious damage in the gas turbine moving blade and stationary blade. In the prior art gas turbine, however, there has been taken no effective countermeasure for preventing the foreign matters from coming in the turbine while the by-pass valve 08 is opened.